The present invention relates to a flat panel display which emits light by causing electrons emitted from an electron-emitting source to bombard on a phosphor screen and, more particularly, to a flat panel display which uses nanotube fibers as an electron-emitting source.
In recent years, a flat panel display such as a field emission display (FED) or a field emission display which uses nanotube fibers, e.g., carbon nanotubes, as the electron-emitting source of a flat vacuum fluorescent display has been proposed and attracts attention.
A carbon nanotube is a material with a structure in which a single graphite layer is cylindrically closed and a five-membered ring is formed at the distal end of the cylinder. As the carbon nanotube is chemically stable, it is not easily influenced by a residual gas. The typical diameter of the carbon nanotube is as very small as 10 nm to 50 nm to provide a material having a high aspect ratio. Hence, the carbon nanotube has a high field-emission performance.
Regarding a flat panel display which uses the above carbon nanotube as the electron-emitting source, an example which uses an electron-emitting source obtained by fixing, to a cathode with a conductive adhesive, a needle-like graphite column which has a length of several μmm to several mm and is made of a group of carbon nanotubes, and an example which uses an electron-emitting source formed by printing by using a paste mixed with columnar graphite are available (e.g., see Japanese Patent Laid-Open No. 11-162383).
According to the characteristic feature of a flat panel display having carbon nanotubes as the electron-emitting source, it has low power consumption due to the high field emission efficiency and thus has high brightness.
The basic arrangement of the flat panel display will be described with reference to FIG. 17.
In the flat panel display, the screen is formed by arraying a plurality of pixels in a matrix. This display has a vacuum envelope with a front glass plate 108 which is at least partly transparent and a substrate 101 opposing the front glass plate 108, a cathode 102 formed on the substrate 101, an electron-emitting source 103 formed at a predetermined region of the cathode 102, a gate electrode 105 having an electron-passing hole and opposing the substrate 101 to be separate from the cathode 102, and a phosphor screen 107 and an anode electrode 106 formed on the surface of the front glass plate 108. An insulating substrate 104 is provided between the cathode 102 and gate electrode 105.
The operation of the flat panel display will be described.
A voltage is applied between the gate electrode 105 corresponding to the electron-emitting source 103 and the cathode 102 such that the gate electrode 105 has a positive potential. This potential difference concentrates the electric field at the electron-emitting source 103, so that electrons are emitted.
The emitted electrons are accelerated toward the anode electrode 106 by applying a voltage between the anode electrode 106 and cathode 102, and bombard on the phosphor screen 107. Thus, the phosphor screen 107 emits light. When the phosphor screen 107 is constituted by three portions corresponding to the three primary colors of light consisting of R (red), G (green), and B (blue), color display can be performed.
The conventional flat panel display, however, has the following problems.
When the flat panel display is driven, for example, while a voltage which is positive with respect to cathodes is constantly applied the anode electrode, the cathodes are sequentially scanned in a pulse-like manner. When a predetermined cathode is selected, a voltage which is positive with respect to the cathode is applied, in accordance with an image to be displayed, to a gate electrode corresponding to each pixel. In this driving circuit, the voltage to be applied to the gate electrodes must be high. Hence, when the voltage between the gate and cathode changes, the anode current changes, and consequently the display uniformity within the panel fluctuates. Also, as the voltage to be applied to the gate electrode is high, the power consumption also increases.
An electron-emitting source provided to each cathode is formed by forming, on the surface of a cathode substrate, a film of a paste including, e.g., carbon nanotubes by printing such as screen printing, or thermal CVD. The surface of the electron-emitting source formed by, e.g., screen printing, is brought in contact with the gate electrode substrate. Accordingly, during alignment, the surface of the electron-emitting source rubs against the lower surface of the gate electrode surface, and is accordingly damaged. When carbon nanotubes form a film by thermal CVD, the film is brought into contact with the gate electrode substrate in the same manner as in the case wherein the film is formed by printing. Hence, the surfaces of the carbon nanotubes constituting the electron-emitting source are damaged. As a result, the display uniformity within the panel fluctuates.
A stray capacitance is formed between the cathode and the gate electrode substrate. When the intersecting area of the space sandwiched by the cathode and gate electrode is large, the stray capacitance increases, and the load capacitance occurring when the flat panel display is driven increases. The response speed decreases, and consequently the display uniformity within the panel fluctuates.